This invention relates to an improved bell and spigot slip-joint assembly.
A bell and spigot slip-joint assembly comprises a spigot extending into the bell end of another tubular member, and a gasket ring tightly and sealingly received between the interior surface of the bell end and the exterior surface of the spigot. Such a joint can separate under pressure.
Heretofore, concrete thrust blocks have been used to prevent separation. However, concrete thrust blocks are expensive and labor intensive to install. An alternative to concrete thrust blocks are rings that circumferentially bite into the spigot by means of knobs or serrations. Such a ring is connected to a restraint ring at the bell. A high density polyethylene spigot can be sensitive to point loads via environmental stress cracking. Environmental stress cracking occurs where local stress is high due to point impingement. High density polyethylene can also slip with respect to the knobbed or serrated ring by means of relaxation creep. Finally, ground water corrosion of the serrations or knobs may cause failure of the ring in restraining the spigot.